Formation of N(epsilon)-(carboxymethyl)lysine and loss of lysine in casein glucose-fatty acid model systems

Dual functional roles of nutritional additives in nutritional fortification and safety of thermally processed food: Potential, limitations, and perspectives

The Maillard reaction (MR) has been established to be a paramount contributor to the characteristic sensory property of thermally processed food products. Meanwhile, MR also gives rise to myriads of harmful byproducts (HMPs) (e.g., advanced glycation end products (AGEs) and acrylamide). Nutritional additives have attracted increasing attention in recent years owing to their potential to simultaneously improve nutritional quality and attenuate HMP formation. In this manuscript, a brief overview of various nutritional additives (vitamins, minerals, fatty acids, amino acids, dietary fibers, and miscellaneous micronutrients) in heat-processed food is provided, followed by a summary of the formation mechanisms of AGEs and acrylamide highlighting the potential crosstalk between them. The main body of the manuscript is on the capability of nutritional additives to modulate AGE and acrylamide formation besides their traditional roles as nutritional enhancers. Finally, limitations/concerns associated with their use to attenuate dietary exposure to HMPs and future perspectives are discussed. Literature data support that through careful control of the addition levels, certain nutritional additives possess promising potential for simultaneous improvement of nutritional value and reduction of AGE and acrylamide content via multiple action mechanisms. Nonetheless, there are some major concerns that may limit their wide applications for achieving such dual functions, including influence on sensory properties of food products, potential overestimation of nutrition enhancement, and introduction of hazardous alternative reaction products or derivatives. These could be overcome through comprehensive assay of dose-response relationships and systematic evaluation of the diverse combinations from the same and/or different categories of nutritional additives to establish synergistic mixtures.

Effect of edible oil type on the formation of protein-bound Nε-(carboxymethyl)lysine in roasted pork patties

Protein-bound Nε-(carboxymethyl)lysine (CML), an advanced glycation end product within meat products, poses a potential health risk to humans. The objective of this study was to explore the impact of various edible oils on the formation of protein-bound CML in roasted pork patties. Eleven commercially edible oils including lard oil, corn oil, palm oil, olive oil, flaxseed oil, blended oil, camellia oil, walnut oil, soybean oil, peanut oil, and colza oil were added to pork tenderloin mince, respectively, at a proportion of 4 % to prepare raw pork patties. The protein-bound CML contents in the pork patties were determined by HPLC-MS/MS before and after roasting at 200 °C for 20 min. The results indicated that walnut oil, flaxseed oil, colza oil, olive oil, lard oil, corn oil, blended oil, and palm oil significantly reduced the accumulation of protein-bound CML in pork patties, of which the inhibition rate was in the 24.43 %-37.96 % range. Moreover, the addition of edible oil contributed to a marginal reduction in the loss of lysine. Meanwhile, glyoxal contents in pork patties were reduced by 16.72 %-43.21 % after roasting. Other than blend oil, all the other edible oils restrained protein oxidation in pork patties to varying degrees (between 20.16 % and 61.26 %). In addition, camellia oil, walnut oil, and flaxseed oil increased TBARS values of pork patties by 2.2-8.6 times when compared to the CON group. After analyzing the fatty acid compositions of eleven edible oils, five main fatty acids (palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid) were selected to establish Myofibrillar protein-Glucose-fatty acids systems to simulate the roasting process. The results showed that palmitic acid, oleic acid, linoleic acid, and linolenic acid obviously mitigated the formation of myofibrillar protein-bound CML, exhibiting suppression rates ranging from 10.38 % to 40.32 %. In conclusion, the addition of specific edible oil may curb protein-bound CML production in roasted pork patty by restraining protein or lipid oxidation, reducing lysine loss, and suppressing glyoxal production, which may be attributed to the fatty acid compositions of edible oils. This finding provides valuable guidance for the selection of healthy roasting oils in the thermal processing of meat products.

Lipid Peroxidation Has Major Impact on Malondialdehyde-Derived but Only Minor Influence on Glyoxal and Methylglyoxal-Derived Protein Modifications in Carbohydrate-Rich Foods

In the present work, the contribution of lipid peroxidation on modifications of lysine and arginine residues of proteins was investigated. Lipid peroxidation had a major impact on malondialdehyde-derived protein modifications; however, the influence on glyoxal and methylglyoxal-derived modifications in flat wafers was negligible. Therefore, vegetable oils (either linseed oil, sunflower oil, or coconut oil) were added to respective batters, and flat wafers were baked (150 °C, 3-10 min). Analysis of malondialdehyde indicated oxidation in linseed wafers, which was supported by the direct quantitation of three malondialdehyde protein adducts in the range of 0.09-23.5 mg/kg after enzymatic hydrolysis. In contrast, levels of free glyoxal and methylglyoxal were independent of the type of oil added, which was in line with the analysis of 13 advanced glycation end products. Comprehensive incubations of 40 mM N²-t-Boc-lysine (100 mM phosphate buffer, pH 7.4) with either 10% oil or an equimolar concentration of carbohydrates led to magnitudes higher (10³-10⁵) amounts of N⁶-carboxymethyl lysine, N⁶-glycolyl lysine, and N⁶-carboxyethyl lysine in the latter. Furthermore, malondialdehyde exceeded glyoxal and methylglyoxal in incubations of pure oils at 150 °C by factors of 30 and 100, respectively.

The association of N ε-Carboxymethyllysine with polyunsaturated and saturated fatty acids in healthy individuals

Red blood cell (RBC) fatty acids status is used as a biomarker of dietary intake of fats however, there is still a paucity of evidence regarding individual fatty acids and modulation of endogenous advanced glycation end-product (AGE) levels. Due to membrane PUFA being a well-known target for peroxidation, we hypothesized that cellular PUFAs are positively associated with circulatory N ε-carboxymethyllysine (CML) that is also influenced by glyoxal (GO) levels in healthy cohorts. To test this, we investigated the association between RBC fatty acids and circulatory AGEs biomarkers in healthy individuals. The results showed a negative association between saturated fatty acids (SFA) and CML and stepwise multivariate regression analysis indicated stearic acid was negatively associated with CML levels (β = -0.200, p=0.008) after adjusting for age, BMI, and gender. In addition, stearic acid: palmitic acid ratio was also negatively correlated with plasma concentrations of CML (rp= -0.191, p = 0.012) and glucose (rp= -0.288, p = 0.0001). Polyunsaturated fatty acids (PUFA) showed a positive association with CML levels particularly, docosapentaenoic acid, γ-Linolenic acid, arachidonic acid, and docosadienoic acid. However, these associations were not evident after the multiple regression analysis adjusted for age, BMI, and gender. A strong negative correlation (rp= -0.98, p< 0.0001) between total PUFA and total SFA was observed. Furthermore, the SFA:PUFA ratio was inversely correlated with CML (rp= -0.227, p< 0.003). Overall, this study indicates that different fats and their combinations may influence the formation of AGEs and that carefully controlled interventions are required to further test this hypothesis.

Role of saturated and unsaturated fatty acids on dicarbonyl-albumin derived advanced glycation end products in vitro

Glycation is a non-enzymatic reaction that occurs between the free amino group of proteins and reducing sugars and/or lipids, leading to the formation of advanced glycation end products (AGEs). The reaction also produces reactive oxygen species that have detrimental effects on cellular and extracellular proteins. Aminoguanidine is a known inhibitor of AGEs, and some fatty acids are known to have a beneficial role in vivo by reducing inflammation and oxidative stress. However, the role of fatty acids on AGE formation has not been thoroughly reported. We investigated the role of a range of fatty acids in the formation of AGEs and their reactive intermediates using an in vitro BSA-dicarbonyl model. The model assessed a time-dependent (0-72 h) and dicarbonyl concentration (0-2 mM) -dependent studies for the optimal formation of AGEs. A 72 h time point was found to be optimal for the reaction of BSA with either methylglyoxal (MGO) or glyoxal (GO) to generate AGE-BSA complexes. When arachidonic, eicosapentaenoic or docosahexaenoic acids were included in the reaction, a significant decrease in protein-bound fluorescent AGEs was seen compared to the respective controls. In contrast, saturated and 18 carbon polyunsaturated fatty acids showed no significant activity. Liquid chromatography-mass spectrometry (LC-MS/MS) analysis showed saturated fatty acids significantly decreased the production of N^ε-carboxymethyllysine (CML) and N^ε-carboxyethyllysine (CEL) from GO and MGO models, respectively, whilst increasing methylglyoxal-derived hydroimidazolone (MG-H1). In contrast, arachidonic, eicosapentaenoic and docosahexaenoic acids did not significantly change either CEL or MG-H1 compared to no treatment controls whilst significantly reducing CML levels.

Adverse Effects of Thermal Food Processing on the Structural, Nutritional, and Biological Properties of Proteins

Thermal processing is one of the most important processing methods in the food industry. However, many studies have revealed that thermal processing can have detrimental effects on the nutritional and functional properties of foods because of the complex interactions among food components. Proteins are essential nutrients for humans, and changes in the structure and nutritional properties of proteins can substantially impact the biological effects of foods. This review focuses on the interactions among proteins, sugars, and lipids during thermal food processing and the effects of these interactions on the structure, nutritional value, and biological effects of proteins. In particular, the negative effects of modified proteins on human health and strategies for mitigating these detrimental effects from two perspectives, namely, reducing the formation of modified proteins during thermal processing and dietary intervention in vivo, are discussed.

N ε-(carboxymethyl)lysine formation from the Maillard reaction of casein and different reducing sugars

Dietary advanced glycation end products (AGEs) are involved in the pathogenesis of diabetic complications, atherosclerosis, and kidney disease. Formation of N ^ε-(carboxymethyl)lysine (CML), a well-known AGEs, was evaluated from the reaction of casein from bovine milk with different reducing sugars (glucose, tagatose, and xylose) at various sugar concentrations and heating temperatures (75 and 120 °C) used in food processing to determine the best sweetener to be used in dairy products. The concentration of CML was measured using an enzyme-linked immunosorbent assay. Additionally, SDS-PAGE was carried out to observe the changes in the molecular weight of casein. The results reveal that tagatose leads to a lower CML concentration at 75 °C than glucose or xylose, whereas no significant differences are observed at 120 °C. We conclude that it would be more appropriate to use tagatose rather than glucose or xylose as a sweetener, considering the AGEs contents in heat-treated dairy products.

Limitation of Maillard Reactions in Lactose-Reduced UHT Milk via Enzymatic Conversion of Lactose into Galactooligosaccharides during Production

Lactose-hydrolyzed (LH) ultrahigh temperature (UHT) processed milk is more prone to Maillard reactions and formation of advanced glycation end products (AGEs) during processing and storage than conventional (CON) UHT milk because of the presence of free galactose and glucose. Commercially available β-d-galactosidases with transgalactosylating activity can incorporate galactose into galactooligosaccharides (GOSs) and potentially limit Maillard reactions in this lactose-reduced GOS-containing milk. The aim of this study was to examine the extent of Maillard reactions in a lactose-reduced GOS milk compared to LH and CON milk after UHT processing. The GOS milk had significant lower levels of lysine- and arginine-derived AGEs compared to LH milk, while their concentrations were similar to those found in CON milk. The total concentration of measured Arg-derived AGEs was similar to the total concentration of Lys-derived AGEs in the three types of milk, indicating that Arg is an important source of AGEs in milks. Interestingly, the GOS milk generated threefold higher concentrations (up to 330 ± 6 μM) of 3-deoxyglucosone (3-DG, a C6 α-dicarbonyl). These results demonstrate that GOS milk could be a potential alternative for LH milk for lactose-intolerant individuals, although further studies are needed to understand the increased formation of 3-DG in GOS-containing milk.

Effect of fatty acids and triglycerides on the formation of lysine-derived advanced glycation end-products in model systems exposed to frying temperature

Lysine-derived advanced glycation end-products (AGEs), including N^ε-carboxymethyllysine (CML), N^ε-carboxyethyllysine (CEL) and pyrraline, are prevalent in processed foods. The impact of lipids on AGE formation is still contentious and most of our current knowledge is based only on CML. Little is known about how lipids impact the formation of CEL and pyrraline, or their involvement in formation pathways. This study investigated the effect of lipids (fatty acids and triglycerides) on the formation of CML, CEL and pyrraline simultaneously in model systems subjected to frying temperature. The results showed the presence of the lipids promoted the formation of CML, CEL and pyrraline. The promotion effects on CML and CEL were not dependent on the unsaturation degree and addition level (50, 100 or 150 μmol) of lipid, while pyrraline formation depended on lipid type (fatty acids vs. triglycerides) and level. The concentration of CML and CEL was statistically correlated with the concentration of glyoxal (GO) and methylglyoxal (MGO), respectively. The pyrraline concentration was statistically correlated with fructoselysine concentration. These results suggested that lipids promote the formation of lysine-derived AGEs by impacting the generation of Amadori products and α-dicarbonyl compounds. This information may be useful for optimizing the formulation and processing conditions to create tastier and healthier foods.

Fatty acids and triglycerides impact lysine-derived AGE formation through modulating the formation of α-dicarbonyl compounds and Amadori products.

The digestibility of hydrothermally-treated bovine serum albumin glycated by glyoxal

The digestion of dietary advanced glycation end products (AGEs) largely determines their absorption in humans. To help elucidate the health effects of dietary AGEs, changes in the digestive behavior of bovine serum albumin (BSA, dietary protein) caused by glycation derived from glyoxal (GO, an important precursor of AGEs) in a simulated food heating system have been investigated. The hydrothermal aggregation of BSA was suppressed by GO derived glycation, generating glycated aggregates of loose and branched structures, according to dynamic light scattering (DLS), circular dichroism (CD) spectroscopy, free sulfhydryl group, transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS) results. Analysis of protein digests showed that glycation reduced the gastric and gastrointestinal digestibility of BSA and the bioavailability of all seven detected amino acids. A comparative analysis of the distribution of CML and lysine in glycated BSA digests with different molecular weights showed that carboxymethylation directly blocked the action of proteases on Lys residues.

The overall gastrointestinal digestibility of hydrothermally-treated bovine serum albumin drops dramatically following GO-derived glycation.

Digestibility of Glyoxal-Glycated β-Casein and β-Lactoglobulin and Distribution of Peptide-Bound Advanced Glycation End Products in Gastrointestinal Digests

This work reports the influence of glyoxal (GO)-derived glycation on the gastrointestinal enzymatic hydrolysis of β-lactoglobulin and β-casein. Reduced digestibility of glycated proteins was found in both gastric and intestinal stage. Distribution of Maillard reaction products in digests with different molecular weight ranges was investigated subsequently. The colorless and brown MRPs largely presented in the digests smaller than 20 kDa. However, the resistance of fluorescent advanced glycation end products (AGEs) to enzymatic hydrolysis gradually increased during glycation, rendering fluorescent AGEs largely present in the digests larger than 20 kDa. No free N (ε)-carboxymethyllysine (CML) was detected in digests. The relative amount of CML in digests larger than 1 kDa was higher than that of Lys, demonstrating the hindrance of CML to enzymatic hydrolysis. This study highlights the resistance of GO-derived AGEs to digestive proteases via blockage of tryptic cleavage sites or steric hindrance, which is a barrier to the absorption of dietary AGEs.

Dairy products and the Maillard reaction: A promising future for extensive food characterization by integrated proteomics studies

Heating of milk and dairy products is done using various technological processes with the aim of preserving microbiological safety and extending shelf-life. These treatments result in chemical modifications in milk proteins, mainly generated as a result of the Maillard reaction. Recently, different bottom-up proteomic methods have been applied to characterize the nature of these structural changes and the modified amino acids in model protein systems and/or isolated components from thermally-treated milk samples. On the other hand, different gel-based and shotgun proteomic methods have been utilized to assign glycation, oxidation and glycoxidation protein targets in diverse heated milks. These data are essential to rationalize eventual, different nutritional, antimicrobial, cell stimulative and antigenic properties of milk products, because humans ingest large quantities of corresponding thermally modified proteins on a daily basis and these molecules also occur in pharmaceuticals and cosmetics. This review provides an updated picture of the procedures developed for the proteomic characterization of variably-heated milk products, highlighting their limits as result of concomitant factors, such as the multiplicity and the different concentration of the compounds to be detected.

Effects of raw meat and process procedure on Nε-carboxymethyllysine and Nε-carboxyethyl-lysine formation in meat products

This work aimed to investigate the effects of stored raw meat and process procedures on N^ε-carboxymethyl-lysine (CML) and N^ε-carboxyethyl-lysine (CEL) generation in meat products. Meat products of raw pork were sterilized and pasteurized at different storage times (0-4 months) and the CML/CEL contents were determined. The results showed that the extent of lipid and protein oxidation of raw pork increased with increasing storage time. A linear correlation was found between thiobarbituric acid-reactive substances value/carbonyl content and CML/CEL in sterilized meat products, indicating that stored raw pork could promote CML/CEL formation under high temperature processing. Furthermore, mild heating temperatures seemed to favor CML formation, while high temperature could accelerate CEL generation. Therefore, formation kinetics of CML and CEL might be different for different process procedures. These results suggested that stored raw meat and processing temperature could significantly affect CML and CEL generation in meat products.

Glycation Reactions of Casein Micelles

After suspensions of micellar casein or nonmicellar sodium caseinate had been heated, respectively, in the presence and absence of glucose for 0-4 h at 100 °C, glycation compounds were quantitated. The formation of Amadori products as indicators for the "early" Maillard reaction were in the same range for both micellar and nonmicellar caseins, indicating that reactive amino acid side chains within the micelles are accessible for glucose in a comparable way as in nonmicellar casein. Significant differences, however, were observed concerning the formation of the advanced glycation end products (AGEs), namely, N(ε)-carboxymethyllysine (CML), pyrraline, pentosidine, and glyoxal-lysine dimer (GOLD). CML could be observerd in higher amounts in nonmicellar casein, whereas in the micelles the pyrraline formation was increased. Pentosidine and GOLD were formed in comparable amounts. Furthermore, the extent of protein cross-linking was significantly higher in the glycated casein micelles than in the nonmicellar casein samples. Dynamic light scattering and scanning electron microscopy showed that glycation has no influence on the size of the casein micelles, indicating that cross-linking occurs only in the interior of the micelles, but altered the surface morphology. Studies on glycation and nonenzymatic cross-linking can contribute to the understanding of the structure of casein micelles.

Kinetics of N(ε)-(carboxymethyl)lysine formation in aqueous model systems of sugars and casein

This study investigated the formation of N(ε)-carboxymethyllysine (CML) in two caseinate solutions containing: (1) glucose, (2) lactose, each heated at 120 °C and 130 °C. At both heating temperatures, CML concentration in lactose-caseinate solution was higher than in glucose-caseinate solution. In both solutions, more CML was formed at 130 °C than at 120 °C. Using multiresponse modelling, two degradation routes for the sugars were confirmed: (1) isomerisation of glucose or lactose and subsequent degradation via Lobry de Bruyn-Alberda van Ekenstein (LA) arrangement; (2) the Maillard reaction between the reducing sugar and lysine residues. Modelling results suggested that CML was not formed from oxidation of the reducing sugars, but from the Maillard reaction via the Amadori rearrangement product. Since CML appeared to be thermally unstable under the current study conditions, it may not be a perfect indicator for heat damage of processed foods. This is the first study in which CML formation was linked to available information on the Maillard reaction via multiresponse modelling.

Natural compounds from grape by-products enhance nutritive value and reduce formation of CML in model muffins

This study had the objective of determining the effects of the addition of different ingredients and grape by-products (GP) to muffins on CML content. It was found that ingredients, such as salt, baking powder and protein-rich components, reduced CML from 50% to 86%. The use of all ingredients simultaneously caused the highest reduction in CML, suggesting synergistic effects in the muffin formula. Raw cane sugar produced higher amounts of CML than refined sucrose, probably due to metal-ion mediated degradation of fructoselysine. The CML content was correlated with the level of oleic acid at -0.829 and with the level of linoleic acid at 0.913. Muffins enriched with appropriate levels of GP (20%) showed a lowering of the CML level and no significant changes in the sensory profile. GP added to the model system with protein-rich ingredients resulted in the weakest inhibitory effects, probably due to the polyphenol-protein binding mechanism.

The colorants, antioxidants, and toxicants from nonenzymatic browning reactions and the impacts of dietary polyphenols on their thermal formation

Nonenzymatic browning reactions proceed with the starting reactants of sugar and/or protein during thermal processing and storage of food.

Effects of hydrophobic and ionic interactions on glycation of casein during Maillard reaction

This study aimed to investigate the effects of hydrophobic and ionic interactions on glycation of native and high-shear treated casein during heating. Casein-epicatechin and casein-calcium complexes were formed and glycated with glucose at different temperatures ranging from 70 to 150 °C in solution and dry states. Furosine, acid derivative of N-ε-fructoselysine (FL), and N-ε-carboxymethyl lysine (CML) were measured as indicators of early and advanced glycation, respectively. CML concentrations of casein-epicatechin and casein-calcium complexes heated in solution were significantly lower as compared to the control (p < 0.05). For instance, 182 ± 9.78 μg/g of CML formed in the control, while CML concentrations were 136 ± 10.7 and 101 ± 7.37 μg/g in casein-epicatechin and casein-calcium complexes, respectively, heated at 150 °C in the solution state. Treatment by high shear microfluidization further decreased the CML formed during heating at 70 °C in dry state. The results suggest that interactions with epicatechin molecule and calcium ion could be a useful strategy to limit advanced glycation of casein under certain conditions.

Effect of raw milk on allergic responses in a murine model of gastrointestinal allergy

Epidemiological studies have shown an association between the consumption of raw farm milk and reduced incidence of allergy. In the present study, we fed untreated raw milk, gamma-sterilised milk, heat-treated milk or water to mice and compared their responses to allergen exposure and challenge treatment in a mouse model of gastrointestinal allergy. From weaning (3 weeks old), groups of BALB/c female mice (n 8) received raw milk, gamma-sterilised milk, heated milk or water via drink bottles, with the control group receiving water. All mice were fed a standard (dairy protein-free) rodent diet. At 6 and 8 weeks, groups were given intra-peritoneal injections with ovalbumin (OVA)/alum to sensitise them to the antigen. Controls were sham immunised. At week 10, mice were fasted and challenged four times on alternate days by intra-gastric administration with 50 mg OVA or saline. Levels of bacteria and milk proteins were assessed in milk samples. Mouse serum levels of specific IgE, IgG1 and IgG2a antibodies and mouse mast cell protease-1 (MMCP-1) were determined. Cytokine responses to 48 h activation with OVA were measured in cultured splenocytes from mice. Sterilised and heated milks contained no viable bacteria and reduced detectable levels of many milk proteins, in contrast to raw milk. Mice drinking raw milk had highest serum MMCP-1 and specific-OVA IgE responses. Cultured splenocytes from OVA-primed mice produced similar levels of IL-4 in response to the antigen; however, IL-10 levels were highest from mice drinking raw milk. Overall, the present study adds to the evidence that consuming different types of milk can affect allergic responses to a non-related dietary antigen.

Mass Spectrometry-based Quantification of Proteins and Peptides in Food

The application of quantitative proteomics to food analysis is in its infancy. This is partly due to the diverse range of plant and animal species consumed as foods, many of which are not sequenced, making annotation of food proteomes difficult. In addition food processing procedures and interactions with other food components, such as lipids and starch, introduce a diverse range of chemical and conformational changes to proteins, many of which are poorly defined. Mass spectrometry-based molecular profiling has great potential as quality assurance tool for food authenticity and traceability, safety and quality. A driver for the application of quantitative protein mass spectrometry-based methods to food has been the need to develop confirmatory methods for allergen analysis in support of food allergen labelling regulations. In addition to providing rigorous quantitative methodology for complex biomacromolecules, protein mass spectrometry is also allowing us, for the first time, to discover how processing procedures modify the foods we eat at a molecular level. Such knowledge is essential if we are to understand how food processing can be used to optimise the beneficial health effects of foods.

Hydroxyl radical induced by lipid in Maillard reaction model system promotes diet-derived N(ε)-carboxymethyllysine formation

N(ε)-carboxymethyllysine (CML) is commonly found in food, and is considered as a potential hazard to human health. However, the effect of lipids on CML formation in Maillard reaction is still not clarified. In this study, the content of diet-derived CML and its key intermediates, epsilon-fructoselysine (FL) and glyoxal (GO), is determined with high performance liquid chromatography mass spectrum (HPLC-MS) in model system containing lipid compounds. According to the results, hydroxyl radical (OH) induced by Fenton reagent can promote the three pathways of CML formation. Moreover, in the Maillard reaction system, linoleic acid (Lin), oleic acid (Ole) and glycerol trioleate (Tri) can induce more OH·, which promotes CML formation. Their level of promoting CML formation is in the order of Ole>Lin>Tri. On the contrary, glycerol (Gly) can scavenge OH·, which inhibit the CML formation. Finally, it is proved that FL content and GO content decreases with heating time in model system, while CML content increases with heating time. Thus, it is concluded that in the Maillard reaction system lipids can induce more OH·, which promotes the conversion from FL and GO to CML. Our research may contribute to the development of inhibitory methods for diet-derived CML by scavenging OH·.

Review of the characteristics of food-derived and endogenous ne-carboxymethyllysine

Ne-Carboxymethyllysine (CML), a representative of advanced glycation end products (AGEs), is commonly found in food and is considered a potential hazard to human health. Food scientists have begun to investigate the formation of CML in food processes. As the understanding of CML is mainly based on that of endogenous CML from the fields of biology and medicine, this review summarizes the different characteristics of food-derived CML and endogenous CML with respect to food safety, detection methods, formation environment, formation mechanism, and methods for inhibiting the formation of CML. Additionally, future research directions for the study of food-derived CML are proposed, including understanding its digestion, absorption, and metabolism in human health, developing rapid, reliable, and inexpensive detection methods, revealing its relationship with food components and production processes, and controlling the formation of CML through the addition of inhibitors and/or modification of food processing conditions, so as to contribute to the methods for controlling food-derived AGEs.

Immunochemical and mass spectrometric analysis of Nε-(carboxymethyl)lysine content of AGE-BSA systems prepared with and without selected antiglycation agents

The present study was designed to compare surface plasmon resonance (SPR) biosensor, enzyme-linked immunosorbent assay (ELISA), and ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) methods for the analysis of Nε-(carboxymethyl)lysine (CML) in glucose-bovine serum albumin (BSA) model systems and to investigate the possible inhibitory effect of selected compounds (α-tocopherol, ferulic acid, rutin, thiamin, thiamin monophosphate, and thiamin pyrophosphate) on CML formation. The reported levels of CML detected were dependent upon the method of analysis employed. The highest reported concentrations were obtained with the SPR biosensor, whereas the lowest were found by ELISA. However, a high correlation was observed between these two immunochemical procedures. CML concentrations were dependent upon the type and concentration of the candidate CML inhibitor. All inhibitory compounds investigated, with the exception of α-tocopherol, decreased the level of CML formation in the glucose-BSA system.